1. Technical Field of the Invention
The present invention relates generally to a robot control system designed to control a plurality of servomotors for moving articulated arms, etc., and more particularly to an improved structure of a robot control system capable of communicating with position detectors for servomotors through a small number of signal lines.
2. Background of Related Art
FIG. 12 shows a conventional robot control system consisting essentially of the robot driver 9 which controls an operation of the robot 8. The robot 8 includes the rotary encoder 1 and differential drivers 2, 3, and 4. The rotary encoder 1 is an absolute encoder which measures an angular position of a servomotor and outputs, as is well known, A- and B-phase incremental signals A and B and an absolute signal Rx. The A- and B-phase incremental signals A and B and the absolute signal Rx are each converted by the differential drivers 2 to 4 into two signals which are, in turn, transmitted to the robot driver 9 through communication paths 5 to 7, respectively. The signals transmitted through the communication paths 5 to 7 are converted by the differential receivers 10 to 12 into the original A- and B-phase incremental signals and the absolute signal Rx and inputted to the I/F (Interface) 13. The reference numbers 14 to 16 indicate exclusive OR circuits for detecting wire-breakage.
As will be apparent from the above, the encoder 1 of the conventional robot control system is connected to the robot driver 9 through the six signal lines. When the degree of freedom of the robot 8 is, for example, four (4), four servomotors are used, thus requiring four rotary encoders which are connected to the robot driver 9 through a total of twenty four signal lines. When the degree of freedom of the robot 8 is six (6) or eight (8), thirteen six or fourteen eight signal lines are required.
The signal lines are usually tied up in a bundle and lead into the robot 8. The more the signal lines, the thicker the bundle, thus requiring a large amount of space within the robot 8 for leading the signal lines to the servomotors. This results in increased overall size of the robot 8. Additionally, the increase in signal lines will increase the possibility of wire-breakage causing an error in communication between the robot 8 and the robot driver 9.